In traditional rock breaking tools a piston which pneumatically or hydraulically is made to move back and forth in a cylinder is used, where the piston strikes directly or indirectly via for example a drill steel shank against the end of a drilling steel which in turn strikes the rock. By that the piston, which has a relatively large mass, moves quickly towards the drilling steel unwanted dynamic acceleration forces arise in the drilling rig which strive to pull the drilling steel away from the rock.
In order to decrease the above mentioned dynamic acceleration forces efforts have been made with rock breaking tools which contrary to the traditional rock breaking tools have a piston that does not move as far back and forth in the cylinder during transfer of the impact force which also brings about a possibility to increase the impact frequency.
GB 2 047 794 A shows a rock breaking tool where a piston is pretensioned by pressurizing a pressure fluid space on the tool side of the piston, so that the piston is moved in the direction away from the drill steel at the same time as a pressure is built up in an energy storing space on the side of the piston opposite to the drill steel side. By that then depressurizing the pressure fluid space, the piston is released whereby the pressure in the energy storing space forces the piston towards the drill steel whereby a stress pulse strikes the drill steel.
WO 03/095153 A1 shows another rock breaking tool where a piston is pretensioned by pressurizing a pressure fluid space on the tool side of the piston, so that the piston is moved in the direction away from the drill steel at the same time as a pressure is built up in an energy storing space on the side of the piston opposite to the drill steel side. By that then depressurizing the pressure fluid space, the piston is released whereby the pressure in the energy storing space forces the piston towards the drill steel whereby a stress pulse strikes the drill steel.